Durene production



Oct. 9, 1956 R. BENNETT ETAL 2,766,310

DURENE PRODUCTION Filed Sept. 3, 1953 FLASH DRUM I2 C0 PRESSOR DISTILLATION UNIT HEAT A EXCHANGE)? 11 1111 I6 II CHARGE LINE 35 PROPANE I5 BOTTONS HOLDING TANK RENE INVENTORS.

John M. Powers, Raymond A. Speed, Rufus B. Benneff.

A T TORNE' Y.

United States Patent R DURENE PRQDUCTION Rufus B. Bennett, William T. Hunt, Jolm1M. Powers, and Raymond A. Speed, Baytown, Tex., assignors, by mesne assignments, to Esso Research and Engineering Com pany, Elizabeth, N. 1., a corporation of Delaware Application September 3, 1953, Serial No. 378,292

4 Claims. (Cl. 260-674) The present invention relates to aproceiss for recovering high purity durene from a hydrocarbon mixture containing durene.

More particularly, the present invention is directed to a procedure for recovering a product having a high durene content from a hydrocarbon feed stock boiling in the range of 270 to 400 F. and having less than 40% durene and which, upon chilling below the solidification point of durene, produces a durene slurry which is gel-like and difiicult to filter. Typical hydrocarbon feed stocks for the practice of the present invention contain from 5% to approximately 40% durene.

Hydrocarbon fractions containing substantial amounts of durene are available to the petroleum industry. Typical fractions of this type which are formed by hydroforming naphtha fractions and which are suitable for use as feed stocks in the practice of the present invention are illustrated by the following Table I:

The process of the present invention may be described briefly as follows:

A feed stock having a durene content within the range of about 5% to 40% is obtained. If the durene content of a stock is below this range it may be concentrated as by distillation to form a suitable feed stock. The feed stock which may have a boiling range from 270 to 400 F. is diluted with at least of liquefied normally vaporous hydrocarbon of which propaneorethylene may form the major part. The liquefied normally vaporous hydrocarbon may be substantially pure propane, commercial propane, that is propane mixed with a small amount of contaminants such as ethane and butane, or it may be a mixture of propane and substantial amounts of ethylene, or it may be essentially only ethylene. It is to be understood that hereafter in the specification and claims where the expression liquefied norm-ally vaporous hydrocarbon is used, it is intended to embrace by this expression any of the materials or compositions above enumerated. The feed stock diluted with the liquefied normally vaporous hydro-carbon is then chilled to form a slurry of durene crystals which are then readily separated by suitable separating means such as a rotary filter or a basket type centrifuge. The chilling is preferably carried out by partial evaporation of the liquefied normally vaporous hydrocarbon.

As a further improvement it has been found that if the filter cake fraction obtained contains only about 50% 2,766,310 Patented Oct. 9, 1.956

.2 durene with the remainder :mother liquor, this fraction may be transferred to a crystal growing zone without allowing the durene crystals to .melt during :the transfer and then held in this crystallization zone for a time within the range of 4 110241101118 to cause the durene crystals therein to grow .to .a .larger average size with concomitant dissolving of some of the smaller crystals. After maintaining the slurry 'in the holding tank as described, it may then be removed and subjected to a secondseparating step as by the use of a basket centrifuge, the filter cake obtained from the second separating step having a durene con'tentof approximately or greater.

Turning now specifically to the drawing, a feed stock containing approximately 10% durene is charged through inlet line 11 to a distillation unit .A from which an overhead is removed throughline 12 and discarded and the bottoms removed through .line 13 and discarded andfrom which a side .stream having a content of approximately 19% durene is withdrawn through line 14. To the side stream is added a recycle material via line 15 and the mixture then passed through heat exchanger .16 and into a vessel B which serves as a refrigerating and crystal growing unit.

In vessel B a mixture of durene containing feed stock and propane is refrigerated by the evaporation of a portion of said propane. Propane vapors are removedfrom vessel B through compressor inlet line 17 which discharges to compressor 13. The outlet from :the compressor is connected byline .19 to condenser 20 to liquefy the propane. The outlet of condenser 20 is connected by line 21 to distributor 22 within vessel B. Propane from other parts of the system is introducedinto vapor line 17 by means of line 23. If it is necessary or desirable to make up lossesof prop anefrom the system, additional propane may be introduced from any suitable source, not shown, through inlet line 24 discharging into line 21.

Slurry is withdrawn from vessel B through line 25 :and pump 26. Pump 26 discharges through outlet line 27. If desired,.in order .to encourage the growth of the crystals within a vessel B a portion of this slurry may be recycled through line 27'. Slurry from which the crystals are .to be separated is withdrawn through line '28 to centrifuge unit C where it is separated .into .a filter .cake fraction withdrawn through outlet 29 and a filtrate .fraction withdrawn through outlet 30.

The filtrate fraction through line 30 passes to surge tank D from which vaporized propane is removed through line 32 which connects through line 23 to vapor line 17 for recovery of propane. The liquid filtrate is'withdrawn from surge tank D through .outlet line 33 "and pump 34 and passed through line 35 to heat exchanger 16 where it passes in indirect heat exchange with incoming charge stock for precooling the incoming charge stock as previously explained and is then discharged into propane flash drum E. From flash drum E the liquid fraction free from propane is withdrawn through outlet line 36 and is discarded from the system. Propane vapors from flash drum E are discharged through line 3-7 to mompressor inlet line 17.

The filter cake from centrifuge C consisting of approximately 50% crystallized durene discharges through line 29 to holding tank F. Propane vapors from holding tank F are discharged through branch line 38 to line 32 which in turn discharges into compressor inlet line 17. Holding tank 38 is provided with discharge line 39 connected to pump 40. The outlet of pump 40 is provided with recycle line 41 discharging into holding tank F in order to allow slow stirring of the contents of tank F to encourage crystal growth. From discharge line 41 a branch line 42 enables durene slurry to be Withdrawn to centrifuge unit G from which a high purity durene containing filter cake may be dis charged via outlet line 43. From centrifuge G a filtrate fraction is withdrawn through recycle line 15 and is admixed with feed stock in line 14.

The following is given by way of specific example as to the manner in which the system previously described may be operated. A hydroformate mixed feed containing approximately durene is charged to column A from which a heart cut boiling from about 370 to 393 F. and containing 18.8% durene is recovered as the feed stock for the crystallization procedure. Upon passing 100 pounds of the heart out containing approximately 19% through line 14 and heat exchanger 16 it is cooled to a temperature of 45 F. and discharged into slurry tank B. Slurry tank B is maintained at a temperature of approximately -40 F. by the refrigerating efifect caused by the evaporation of propane. The feed may be held in the slurry tank for a time within the range of 1 to 4 hours. B and that passed to centrifuge C contains no less than 10% liquefied propane in order to allow it to be fiuid. Without this amount of diluent the slurry is gel-like and the durene crystals formed are poorly divided and pliable and have poor filtering characteristics. However, by carrying out the crystal growing step in vessel B in the presence of liquefied propane, large, easily separated crystals are obtained. This type of slurry allows a filter cake having approximately 50 weight percent of durene to be readily removed with a one minute centrifuge spin time. This cake is discharged to holding tank P where it may be held for a time within the range of 4 to 24 hours at a temperature of 70 to 110 F. to cause further growth of the average durene crystals with concomitant dissolving of smaller durene crystals, the slurry having such large crystals being centrifuged for a centrifuging time approximately 5 minutes in centrifuge G. By this means a filter cake having a durene purity of at least 95% may be withdrawn from centrifuge G as product. From 100 pounds of feed stock charged to vessel B a 14.5 pound cake having 13.8 pounds of durene may be recovered. The filtrate from centrifuge G recycled through line may consist of approximately 22.5% durene, amount of the recycle being about 22.4 pounds which is returned to the system for further processing.

The amount of diluent required in the practice of the present invention varies with the temperature to which the slurry is cooled, and with the separating means employed. Minimum amounts of propane diluent for several conditions are given in Table II, below:

TABLE II Temperature Means of Separation of Slurry, F.

-40 Centrifugal Filter. 40 Rotary Filter. 60 Centrifugal Filter. 60 Rotary Filter. 80 Centrifugal Filter. 80 Rotary Filter.

Vol. Percent Cs Based on Feed The practice of the present invention having been de- The slurry in tank scribed and illustrated, what is desired to be claimed as new and useful and to be secured by Letters Patent is:

1. A method for recovering a high purity durene fraction from a feed stock boiling in the range of about 270 to 400 F. and containing durene in an amount in the range of 5% to 40% including the steps of chilling said feed stock to a temperature in the range from 40 to 80 F. in the presence of an amount in the range from 10% to 40% of liquefied normally vaporous hydrocarbon to form a readily filterable slurry of durene crystals and mother liquor, separating said slurry to form a filter cake fraction comprising approximately 50% durene crystals, transferring said filter cake fraction without allowing a substantial amount of melting of said durene crystals to a crystal growing zone and maintaining it in said crystal growing zone at a temperature in the range of to 110 F. for at least four hours to allow the growth of durene crystals and subsequently separating therefrom a product having a durene content of no less than about 95%.

2. A method for recovering a high purity durene fraction from a feed stock boiling in the range of 270 to 400 F. and containing durene in an amount in the range of 5% to 40% including the steps of incorporating a substantial amount of liquefied normally vaporous hydrocarbon in said feed stock, allowing a portion of said liquefied normally vaporous hydrocarbon to evaporate to cool said feed stock by evaporative cooling to a temperature in the range from 40 to F. while maintaining sufficient diluent therein to form a slurry of durene crystals containing an amount in the range from 10% to 40% of liquefied normally vaporous hydrocarbon, withdrawing said slurry and centrifuging it in a first centrifuging zone to recover a filter cake consisting of about 50% durene crystals and 50% mother liquor, withdrawing said filter cake and transferring it to a crystal growing zone without allowing any substantial melting of said durene crystals and maintaining it in said crystal growing zone at a temperature within the range of 70 to 110 F. for a time within the range of 4 to 24 hours to cause durene crystals to grow to a larger average size, withdrawing slurry from said crystal growing zone and centrifuging it in a second centrifuging zone to separate a filter cake consisting of approximately durene.

3. A method in accordance with claim 2 in which the filter cake is recovered in the first centrifuging zone by centrifuging for a time of approximately one minute and in which the filter cake is formed in the second centrifuging zone by centrifuging for a time of approximately 5 minutes.

4. A method in accordance with claim 2 in which the liquefied normally vaporous hydrocarbon is propane.

References Cited in the file of this patent UNITED STATES PATENTS 2,383,174 Weir Aug. 21, 1945 2,435,792 McArdle et a1 Feb. 10, 1948 2,540,977 Arnold Feb. 6, 1951 2,623,903 Weaver et al. Dec. 30, 1952 2,665,316 Bennett Jan. 5, 1954 2,683,178 Findlay July 6, 1954 

1. A METHOD FOR RECOVERING A HIGH PURITY DURENCE FRACTION FROM A FEED STOCK BOILING IN THE RANGE OF ABOUT 270* TO 400* F. AND CONTAINING DURENE IN AN AMOUNT IN THE RANGE OF 5% TO 40% INCLUDING THE STEPS OF CHILLING SAID FEED STOCK TO A TEMPERATURE IN THE RANGE FROM -40* TO -80* F. IN THE PRESENCE OF AN AMOUNT IN THE RANGE FROM 10% TO 40% OF LIQUEFIED NORMALLY VAPOROUS HYDROCARBON TO FORM A SEADILY FILTERABLE SLURRY OF DURENE CRYSTALS AND MOTHER LIQUOR, SEPARATING SAID SLURRY TO FROM AFILTER CAKE FRACTION COMPRISING APPROXIMATELY 